1. Field of the Invention
The present invention relates to a preparation for injection containing a lipid A analog or a pharmacologically acceptable salt thereof, and a process for preparing the same.
2. Prior Art
Lipid A, which is the main moiety causing activities of lipopolysaccharide (hereinafter referred to as LPS), has various biological activities such as macrophage stimulation, antitumor effect and pyrogenicity (for example, Haruhiko Takada and Shozo Kotani, Protein, Nucleic Acid and Enzyme, 31(4), 361(1986)).
Various lipid A analogs have recently been synthesized and examined for their biological activities (Yuji Ogawa et al., Metabolism 26(5), 415(1989)). Lipid A analogs originally have the glycolipid structure. Thus most of the lipid A analogs are sparingly soluble or insoluble in water, so that it is difficult to prepare an injection with lipid A analogs. Therefore, various investigations have been carried out in order to obtain a highly transparent aqueous solution thereof. As a result, it has been proposed, for example, to a dd triethylamine, bovine serum albumin, lipids, or the like as a solubilizing agent (Y. B. Kim, et al, Eur. J. Biochem. 31, 230(1972) and R. B. Ramsey, et al, Blood, 56, 307(1980), J. Dijkstra, et al, J. Immunol., 138, 2663(1987)).
Furthermore, JP-A-4-198192 discloses a method employing basic amino acids or polyamines as a solubilizing agent. However, all of the pH of the aqueous solutions in the method are as high as around pH 10.
On the other hand, as a method of dispersing a lipid such as lecithin or the like in water to form aggregates of liposomes or the like, known is a method to add a lipid to a buffer having a pH around neutrality, followed by heating and sonication.
The method of solubilizing lipid A analogs using solubilizing agents is not satisfactory in view of the physical stability in water, chemical stability, pharmacological effects and safety, and hitherto has not been carried out on a practical basis. Moreover, a transparent solution of a lipid A analog could not be obtained also by the method of dispersing a lipid in a buffer having a pH around neutrality followed by sonication. Therefore, it has been eagerly desired to develop a practical injection containing a lipid A analog, that is, an injection which exhibits high transparency in the form of an aqueous solution, has pH ranging in values suitable for injection, and has excellent stability.